1. Field of the Invention
The present invention relates to media sensing, and, more particularly, to a media sensor apparatus using a two component media sensor for media absence detection.
2. Description of the Related Art
A three component media sensor includes a light source and a pair of light detectors, one of the light detectors being positioned to sense reflected diffuse light and a second detector positioned to sense reflected specular light. Such a sensor may be used, for example, to detect the presence of print media and discriminate between media types, such as for example, paper media and transparency media. Such determinations are made by optically measuring the glossiness of the media, or media support surface.
For example, to measure the glossiness, a collimated beam of light is directed towards the media and a reflectance ratio (R) of the detected reflected specular light intensity and the detected diffusively scattered light intensity is calculated. The media sensor is initially calibrated by measuring a reflectance ratio (R0) on a known gloss media. A normalized reflectance ratio (Rn) is calculated using the formula: Rn=(R/R0). Normalized reflectance ratio Rn then is used to identify the media type of an unknown media by a comparison of the normalized reflectance ratio Rn to a plurality of normalized reflectance ratio Rn ranges, each range being associated with a particular type of media, or the absence of media.
Typically, however, a three component media sensor is more expensive than a two component media sensor.
What is needed in the art is a media sensing apparatus that can detect the absence of print media reliably using a two component media sensor.